1. Field of the Invention
This invention relates to an agricultural tractor, and more particularly to an improvement in a propelling transmission for use in an agricultural tractor.
2. Description of the Related Art
A propelling transmission of the type noted above is disclosed in Japanese Patent Publication Kokai H9-240297, for example. In this prior transmission, a main change speed mechanism and an auxiliary change speed mechanism are combined to perform change speed in multiple stages (eight stages). It is proposed in the above publication to connect, in series to the two change speed mechanisms, a high/low change speed mechanism for performing change speed in two stages with a smaller transmission ratio than the transmission ratio between speed stages of the main change speed mechanism.
In the propelling transmission having the above construction, the number of speeds (eight speeds) provided by the combination of the main change speed mechanism and auxiliary change speed mechanism is combined with the change speed in two stages provided by the high/low change speed mechanism. Thus, a total of 16 speeds is provided by the transmission. In addition, an engageable and disengageable super-reduction mechanism may be connected in series to the change speed mechanisms to provide a total of 32 speeds, doubling the above number of speeds, for a forward drive range.
With as many as 32 speeds available as noted above, it is convenient in performing an agricultural operation since speed may be changed by finely defined stages to suit the operation while running at a relatively low speed in a speed range for an operational run. However, the 32 speeds are too many for a speed range for a road run which requires a relatively high speed. Operability and handling convenience are all the worse for the numerous speed stages, which poses a disadvantage in practical use.